A visual 3-D rendering may be obtained on the basis of a signal that comprises a pair of pictures: a left picture and a right picture intended for the left eye and the right eye, respectively, of a viewer. In the case of a video, the signal will comprise a sequence of such picture pairs. The left and right pictures comprised therein may directly be rendered on a stereoscopic display device, which may require a viewer to wear a pair of glasses. A left-eye glass passes a rendered left picture to the left eye. A right-eye glass passes a rendered right picture to the right eye. For example, the display device may alternately display rendered left pictures and rendered right pictures. In that case, the left-eye glass is made transparent when a rendered left picture is displayed, and is opaque otherwise. Similarly, the right-eye glass is made transparent when a rendered right picture is displayed, and is opaque otherwise.
A signal that comprises a pair of pictures, or a sequence of picture pairs that constitutes a 3-D video, as described in the preceding paragraph, is typically generated for a particular rendering context in terms of, for example, screen size and viewing distance. The particular rendering context may be, for example, a cinema with a screen that is 12 meters wide and where viewers are typically sitting at a distance of 18 meters from the screen. In case a rendering context is different from the rendering context for which the signal has been generated, the 3-D video will look different. For example, in case the 3-D video that has been generated for the cinema is rendered on a home video set, a viewer will experience a different visual impression that in the cinema. Depth effects will typically be smaller and, moreover, there may be an apparent depth shift in the sense that an object which appears to be far behind the screen in the cinema appears to be nearly in front of the screen of the home video set.
A viewer, who watches a 3-D video in a private environment, such as at home, may wish to adjust depth effects so as to obtain a rendering that the user experiences as most pleasant. In principle, it is possible to achieve this by means of an interpolation, or an extrapolation, which is based on each pair of images comprised in the 3-D video. In effect, a left picture and a right picture are compared so as to obtain a so-called disparity map expressing differences between these pictures, in particular in terms of horizontal displacement. Depth effects adjustments may be expressed in the form of a modified disparity map, which is used to generate a new pair of images. Such a process of interpolation, or extrapolation, is relatively complex and, therefore, relatively costly. Moreover, such a process may introduce perceptible artifacts, which may be less pleasant to the viewer.
United States patent application published under number 2005/0190180 describes a method for customizing scene content, according to a user or a cluster of users, for a given stereoscopic display. Customization information about the user is obtained. A scene disparity map for a pair of given stereo images is also obtained. An aim disparity range for the user is determined A customized disparity map is generated that correlates with the user's fusing capability of the given stereoscopic display. The stereo images are rendered or re-rendered for subsequent display.